12 g of Mg (at. Mass 24) will react completely with acid to give

Options

A. 1 mole of `O_(2)`
B. `(1) / (2)` mole of `H_(2)`
C. 1 equivalent of `H_(2)`
D. 2 equivalents of `H_(2)`

Answer

To solve the problem of how much hydrogen gas will be produced when 12 g of magnesium reacts completely with an acid, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Molar Mass of Magnesium:**
The atomic mass of magnesium (Mg) is given as 24 g/mol.

2. **Calculate the Number of Moles of Magnesium:**
To find the number of moles of magnesium, we use the formula:
\[ \text{Number of moles} = \frac{\text{Mass of substance}}{\text{Molar mass}} \]
Here, the mass of magnesium is 12 g.
\[ \text{Number of moles of Mg} = \frac{12 \text{ g}}{24 \text{ g/mol}} = 0.5 \text{ moles} \]

3. **Determine the Reaction with Acid:**
Magnesium reacts with acids to produce hydrogen gas. We can consider two types of acids:
- **Monobasic Acid (e.g., HCl):**
\[ \text{Mg} + 2\text{HCl} \rightarrow \text{MgCl}_2 + \text{H}_2 \]
From this reaction, 1 mole of magnesium produces 1 mole of hydrogen gas.

- **Dibasic Acid (e.g., H2SO4):**
\[ \text{Mg} + \text{H}_2\text{SO}_4 \rightarrow \text{MgSO}_4 + \text{H}_2 \]
In this case as well, 1 mole of magnesium produces 1 mole of hydrogen gas.

4. **Calculate the Moles of Hydrogen Produced:**
Since the mole ratio of magnesium to hydrogen is 1:1 in both reactions, the moles of hydrogen produced will also be equal to the moles of magnesium reacted.
\[ \text{Moles of H}_2 = 0.5 \text{ moles of Mg} \rightarrow 0.5 \text{ moles of H}_2 \]

5. **Conclusion:**
Therefore, when 12 g of magnesium reacts completely with an acid, it produces 0.5 moles of hydrogen gas.

### Final Answer:
**12 g of Mg will react completely with acid to give 0.5 moles of hydrogen gas.**